Socially and professionally, most people rely upon video displays in one form or another for at least a portion of their work and/or recreation. With a growing demand for large screens and high definition television (HDTV), cathode ray tubes (CRTs) have largely given way to displays composed of liquid crystal devices (LCDs), light-emitting diodes (LEDs), plasma and front and rear projection systems.
A CRT operates by a scanning electron beam exciting phosphorous-based materials on the back side of a transparent screen, wherein the intensity of each pixel is commonly tied to the intensity of the electron beam. With an LED and plasma display, each pixel is an individual light-emitting device capable of generating its own light. With an LCD display, each pixel is a transient light-modulating device, individually adjusted to permit light to shine through the pixel.
As neither system utilizes a large tube, LCD, plasma and LED screens may be quite thin and often are lighter than comparable CRT displays. The individual nature of each pixel of an LED, plasma or LCD display introduces the possibility that each pixel may not provide the same quantity of light. One pixel may be brighter or darker than another, a difference that may be quite apparent to the viewer.
The human eye is able to perceive subtle differences in light intensity. This poses a challenge to display manufacturers. If the pixels in a display vary greatly in their light-emitting ability, the display will be unacceptable to users.
To avoid such discrepancies in performance, great care is generally applied in the fabrication of LED, plasma and LCD displays in an attempt to ensure that the pixels are as uniform and consistently alike as is possible. Frequently, especially with large displays, quality control measures discard a high percentage of displays before they are fully assembled. As such, displays are generally more expensive than they otherwise might be, as the manufacturers must recoup the costs for resources, time and precise tooling for both the acceptable displays and the unacceptable displays.
Projection systems offer alternatives to LED, plasma and LCD based systems. In many cases, projection display systems are less expensive than comparably sized LED, plasma and LCD display systems. With a front projection system, the image is projected onto a screen from the same side as the viewer. If the viewer stands, sits or otherwise blocks the projection the image will be compromised. Front projection systems are therefore often suspended from the ceiling or mounted high upon a rear wall.
To accommodate the projector, one or more lenses, and reflectors, rear projection displays are typically 18 to 20 inches deep and not suitable for on-wall mounting. A typical rear projection system offering a 55-inch HDTV screen may weigh less than a comparable CRT, but at 200+ pounds it may be difficult and awkward to install and support.
Often, rear projection display devices exhibit average or below-average picture quality in certain environments. For example, rear projection displays may be difficult to see when viewed from particular angles within a room setting or when light varies within the environment. Aside from a theatrical setting, light output and contrast are constant issues in most settings and viewing environments.
Despite advancements in projectors and enhanced lens elements, the lens and reflector design remains generally unchanged and tends to be a limiting factor in both picture quality and overall display system thickness.
A display may also have to contend with two types of contrast—dark room contrast and light room contrast. Dark room contrast is simply the contrast between light and dark image objects in a dark environment such as a theater setting. Light room contrast is simply the contrast between light and dark image objects in a light environment. Front projection systems typically provide good dark room contrast where ambient light is minimized but, as they rely on a screen reflector, they are subject to poor light room contrast due to the interference of ambient light.
Rear projection displays, LED, LCD and plasma typically provide better light room contrast than front projection systems. However, ambient light striking the viewing surface can be an issue for viewers and buying consumers. Ambient light is oftentimes highly variable. For typical consumers, what makes a display attractive is often high contrast in a bright room.
A developing variation of rear projection displays utilizes light guides, such as optical fibers, to route an image from an input location to an output location, and to magnify the image. Such displays may be referred to as light guide screens (“LGS”). Light room contrast and dark room contrast are generally issues that also apply to LGS systems.
Weight, thickness, durability, cost, aesthetic appearance and quality are key considerations for rear projection display systems and display screens. From the manufacturing point of view, cost of production and increased yield are also important.
Hence, there is a need for a rear projection display that overcomes one or more of the drawbacks identified above.